1. Field of the Invention
The present invention relates to liquid crystal display (LCD) devices, and in particular to transflective liquid crystal display devices and fabrication methods thereof.
2. Description of the Related Art
Liquid crystal display (LCD) devices have many advantages such as small volume, light weight and low power consumption, and are applicable in a variety of electronic and communication devices including notebook computers, personal digital assistants (PDA), mobile phones and the like due to lighter weight, thinner profile, and increased portability.
A conventional LCD device includes a pair of substrates with opposing electrodes thereon. A liquid crystal layer is interposed between the pair of substrates. An electric field is applied on the opposing electrodes to control liquid crystal molecular orientations in the liquid crystal layer, thereby displaying desirable images. Two alignment layers are separately interposed between the interfaces between the liquid crystal layer and each substrate, providing initial orientations and pre-tilting status for the molecules in the liquid crystal layer.
Conventional transflective LCD devices can take advantage of the ambient light and back light to provide better quality display images. The transmissive mode can enhance the reflective mode in dark environments to improve brightness. The reflective mode can enhance the transmissive mode in bright environments for power conservation as well as overcoming the washout effect. The distance of light travel in the reflective region is twice as long as the distance of light travel in the transmissive region, the cell gap in the reflective region, however, must differ from the cell gap in the transmissive region, resulting in deterioration of LCD performance, such as variation in brightness and color.
FIG. 1 is a cross section of a conventional transflective LCD device with different cell gaps on the reflective and the transmissive regions respectively. Referring to FIG. 1, in order to solve problems caused by different light travel distances in the transmissive mode and in the reflective mode, different thicknesses of liquid crystal layers 30 are formed on the transmissive region T and the reflective region R respectively. More specifically, a protrusion structure 12 or a bump is formed on the reflective region R of the lower substrate 10. A reflector 14 is formed on the protrusion structure 12. An upper substrate 20 is disposed opposing the lower substrate 10 with a gap therebetween. Therefore, the liquid crystal layer 30 has a first portion corresponding to the transmissive region T thicker than a second portion corresponding to the reflective region R. By combining with quarter wave plates 40 and 45, phase retardation can be compensated between the transmissive region T and the reflective region R. The quarter wave plates 40 and 45 are disposed on outer surfaces of the upper substrate and the lower substrate respectively. Polarizers 50 and 55 are formed on the quarter wave plates 40 and 45 respectively. A back light unit (BLU) 60 is disposed at the bottom of the transreflective LCD device.
Forming the protrusion structure 12 on the lower substrate 10 and then depositing the reflector 14 on the protrusion structure 12, however, require intricate lithography and deposition procedures, causing high production cost and low yield. It is desirable to overcome these and other problems of the related art and to provide transflective LCD devices including T and R regions with different cell gaps that provide both regions with high light modulation efficiency.
U.S. Pat. No. 6,862,058, the entirety of which is hereby incorporated by reference discloses a single gap transflective LCD device. In each pixel, different alignment layers are formed on the reflective region and the transmissive region respectively to reach the same phase retardation. A vertical alignment layer is formed on an active matrix substrate. A mask layer is disposed on the reflective region, thereby exposing transmissive region under UV radiation. The vertical alignment on the transmissive region is transferred to a horizontal alignment layer. The mask layer is then removed. A rubbing procedure is performed on the vertical alignment layer on the reflective region, while leaving a horizontal alignment layer on the transmissive region.